Effect of Boron on Cell Elongation and Division in Squash Roots

Abstract

This work establishes that cessation of root elongation of intact squash (Cucurbita pepo L.) plants is an early result of boron deficiency. Root elongation is slowed by 6 hours and is virtually stopped as early as 24 hours after boron is first withheld from the nutrient solution. As root elongation ceased, cell elongation progressed distally into the region normally occupied by the apical meristem and eventually the meristem became indistinguishable. Differentiation was determined by use of an elongation index in which cell length was compared to cell width. This index ranged from a low of 0.8 in boron-sufficient root meristems to a high of 3 in root meristems grown in a boron-deficient nutrient solution for 98 hours. It is concluded that a continuous supply of boron is not essential for cell elongation but is required for maintenance of meristematic activity. Boron may act as a regulator of cell division in this tissue. treated and were grown in modified Shive nutrient solution containing boron (+B) as described by Albert and Wilson (1). On the 5th day, roots were washed and placed into either freshly prepared modified Shive nutrient solution to which boron was added (+B) or into nutrient solution without added boron (-B). Water for both types of solutions was obtained by passing distilled H2O through a Millipore Milli-Q2 system. Just before placing the plants into +B or -B nutrient solutions, two roots/ plant were marked by placing small India ink marks 10 mm from the root tip. Subsequent root elongation was determined by measuring the distance from the root tip to the mark. Net root elongation was determined after periods of 0,6, 12, 24, 48, 72, and 98 hr of +B and -B treatment and root tips were harvested for histological examination at these times. The terminal 1 cm of each root was excised, fixed in formaldehyde-acetic-acid-alcohol (6), dehydrated, embedded in paraffin, sectioned, and stained with Sharman stain (11).Alexander (2) studied the onset of boron deficiency in squash plants grown in solution culture in which boron was withheld. He examined the roots of boron-deficient plants after periods of 48, 72, and 98 hr of boron deficiency to observe histological effects of the treatment. After 48 hr of boron deficiency, he reported a decrease in the size of the root cap; collapsed, disintegrated, and enlarged cells or groups of cells in the peripheral portions of the stele; and differentiation close to the root meristem. Examination of roots after 98 hr of boron deficiency commonly revealed death of the extremities of the tip. In the region of elongation, individual cells could no longer be recognized. Varying degrees of response were observed in any given experiment.Other workers have questioned whether boron is necessary for either cell elongation or cell division. Alexander (2), Neales (7), and Sommer and Sorokin (8) beginning from the 5th day onward). Measurements made during the first 24 hr of boron deficiency are presented in Figure 1. All points represent means of at least 100 roots. At all...

Synthesis, Salvage, and Catabolism of Uridine Nucleotides in Boron-Deficient Squash Roots

“…Available evidence demonstrates that boron is essential for the normal functioning of root apical meristems (1,3,6,9,15,16,24,31). However, little is known about the sensitivity of root cells in the elongation and differentiation zones to boron deprivation.…”

Essentiality of Boron for Symbiotic Dinitrogen Fixation in Pea (Pisum sativum) Rhizobium Nodules

“…A high meristem B requirement occurs because of the low phloem mobility of B from shoots to other parts of the plant, leading to a higher accumulation of B in leaves (Raven, 1980 imperative (Gupta, 1979); otherwise, a B deficiency occurs in roots, as we also found in B-deficient pea root (data not shown). Approximately 24 h after B was removed from the nutrient solution, root elongation stopped (Cohen and Lepper, 1977), whereas this effect appeared later on the shoots due to the higher concentration of nutrients in leaves (Loomis and Durst, 1991). We also found this effect in pea roots grown in low B, which produced necrotic root tips (Fig.…”

Transport of Boron by thetassel-less1Aquaporin Is Critical for Vegetative and Reproductive Development in Maize

“…Additional roles for B have been proposed in other parts of the cell, such as the plasma membrane and the cytoskeleton, although none have been demonstrated unequivocally (Cohen, 1977;Loomis and Durst, 1992;Cakmak and Römheld, 1997;Dell and Huang, 1997;Power and Woods, 1997;Bassil et al, 2004). However, several genes have been found to be regulated by B levels, suggesting that plants possess mechanisms to sense, respond to, and maintain B homeostasis, either directly or indirectly (Kobayashi et al, 2004;Takano et al, 2006;Camacho-Cristóbal et al, 2008;Ozhuner et al, 2013;Abreu et al, 2014).…”